1. Field of the Invention
The invention relates to a method and a device for treating and monitoring the quality of objects comprising a metal material.
2. The Prior Art
Metal materials are often used in objects or goods due to their properties and the corresponding objects or goods may be made entirely from metal materials or from a combination of metal and non-metal materials. Containers comprising or made from a metal material are an example of this.
Due to the basic strength and dimensional stability of metal materials, such as aluminum, such containers may be designed with thin walls. Amongst other things, containers made from metal materials are also suitable for preserving sensitive contents, such as foodstuffs. In this respect, another advantage is their excellent gas barrier properties or very low permeability to gases, as is the case with aluminum or aluminum materials, for example. The foodstuffs can be prevented from spoiling over time, thereby resulting in a long shelf life for foodstuffs packaged in such containers.
Items or objects comprising a metal material are often treated with a treatment or process fluid. Amongst other things, this might be necessary during the actual production of the objects, such as for cleaning or tempering purposes, in particular for cooling the objects after shaping, etc. Alternatively, such a treatment with a treatment fluid might be carried out for other purposes. An example of this is a treatment of containers incorporating metal material with a heated process fluid for the purpose of pasteurizing a foodstuff contained in the containers. A treatment of an object comprising a metal material does not comprise a coating of the metal material, such as a varnishing or lacquering or the like.
When treating an object made from an uncoated metal material, a change to the metal material may occur in principle during the course of a lengthy or continuous treatment with treatment fluid over time. Such changes might be of a chemical nature, for example due to surface oxidation processes. Chemical-physical changes may likewise be induced at the surface structure due to such treatments with fluids, for example in layers of the metal materials close to the surface. Such superficial changes in a metal material caused by a treatment fluid may occur in particular in the case of treatment methods in which one and the same treatment fluid is used repeatedly for treating the objects. This is primarily because a repeated treatment of objects with the same treatment fluid can lead to changes in the chemical composition of the treatment fluid. A treatment fluid chemically altered in this manner can in turn lead to changes close to the surface of a metal material during the course of a treatment, at most leading to discoloration of the metal material.
In the case of metal materials, a change in composition or a change in the surface structure of a metal material is often accompanied by a visually perceptible or evident change to the color of the material. This often depends on the type of change to a metal material, which in turn is often dependent on the properties and composition of the treatment fluid. In the case of treating an object containing an uncoated aluminum material with an aqueous treatment fluid, a so-called wet storage stain can occur, for example. Such treatments with a heated, aqueous treatment fluid are often carried out for the purpose of pasteurizing foodstuffs packaged in aluminum containers.
In principle, such changes do not always impair the function of the object or article comprising the metal material, being merely changes close to the surface. However, perceptible discoloration of objects or products is often perceived by consumers as meaning a reduction in quality or even as a possible product fault. Such objects are often no longer viewed as acceptable by consumers and a discolored object or product may then no longer be commercially usable, for example, or may be so but under limited conditions.
This being the case, especially from a commercial point of view, it is in particular problematic if such changes, for example discoloration, during a treatment go unnoticed or are not noticed until some time after they actually occurred. In modern mass production, high batch quantities are often produced in a continuous process. If a change during a process goes undetected or is detected late on, it may be that a whole batch of objects is substandard. For this reason, there is a need for means for monitoring production processes involving a treatment of objects incorporating metal materials with a fluid, in, particular an aqueous treatment fluid.